Rheostat



May 7, *1935. E. w Klar-'ABER ET AL n r2,000,849

RHEOSTAT Filed July 15, 1932 I 2 Sheets-Sheet l May 7, 1935 E. w. KIs-:FABER Er AL 2.000.849

RHEOSTAT Filed July 15, 1932 -2 Sheets-Sheet 2 [acier-ar" lian/Wi@ Patented May 7, 1935 UNTTED4 STATES mos'iwr u Edwin W. Kiefaber and Josef Doen', Philadelpilla, Thomas Barclay Whitson, Moylan, and

William B.

, Norwood, Pa., assignors of fty one-hundredths to James G. Biddle,

tradingasJamesG.

Biddle Company, Philadelphia, Pa., and ilfty one-hundredths to Rubicon Company, Philadelphia, Pa., a corporation of Pennsylvania Application July 15, 1932, Serial lilo. 622,738-

9 Claims.

This invention relates to rheostats and more particularly to rheostats of the slider type. wherein a slidable contact member is movable along a slide bar spaced from a resistance winding which is in the form of a helical coil wound on an insulating supporting mandrel, the contact member slidably engaging the resistance winding. The slidable contact member may be actuated directly or lt may have operatively associated with it a rotatable screw shaft which, when rotated, causes the contact member to move. 'Ihis type of rheostat may be termed a screw-slider type.

The principal object of the invention is to provide a device of this character which is simple in construction, compact, mechanically durable, neat and attractive in appearance, capable -of economical manufacture, and eilicient in operation. 'Ihis object is achieved by virtue of certain distinctive features of construction which are Y. exemplined for the purpose of disclosure on the accompanying drawings, in which Fig. l is a side elevational view of a slider" type rheostat embodying the features -of the 1nvention;

Fig. 2 is a sectional view along line 2 2 of Fis. l;

Fig. 3 is a detail sectional view along line 3 3 of Fig. 2;

Fig. 4 is a detail face view of the underside of the slidable contact member;

Fig. 5 is a partial elevational and sectional view of a "screw-slider type rheostat embodying the features ofthe invention;

Fig. 6 is a sectional view of the entire rheostat along line 6 8 of Fig. 5; and

Fig. 7 is a detail face view of the underside of the slidable contact member.

Referring first to Figs. 1 to 4 and particularly to Fig. l, there is illustrated a slider type rheostat which comprises generally a pair of supporting members I, an insulating supporting mandrel 2, resistance winding 3 wound upon the mandrel, slide bar I, and the slidable contact member or assembly 5. This general construction is not broadly new, but the present invention resides in certain specific features now to be described.

In the present instance, the supporting members I preferably take the form of metallic `end walls having bent feet or attachment portions 6. The supporting mandrel 2 preferably takes the form of a porcelain tube, as illustrated more clearly in Fig. 2, but it will be understood that this member may be formed of any suitable insulating material. The tubular mandrel is not (Cl. 21H-62) A l: directly attached to the end walls I, the ends of the mandrel merely contacting the end walls, but

being free of mechanical connection therewith.

A pair of flat metallic straps l are wrapped tightly about the mandrel at the ends of the resistance winding. The ends of the metallic straps are bent downward into parallel relation with each other and are secured by means of suitable bolts 8, the bolts passing through the strap ends, as will be clearly understood. The ends of the resistance winding pass under straps l and are secured by the bolts 8, as illustrated. This construction eiects good electrical contact between the ends of the winding and the flat metallic straps. It also prevents the wound resistance element from loosening or unwinding on the mandrel, and thereby secures the resistance element as a whole upon its supporting mandrel. Straps 1 are each formed so as to provide at least one integral attachment extension 9. In the present instance, only one such extension, located at the top of each strap, is utilized. The angularly bent end Ill of each attachment extension is disposed in parallel relation with its associated supporting wall I and is rigidly secured thereto by bolt II and insulated therefrom by suitable insulating washers I2, and an insulating bushing (not visible). v

In accordance with the present invention, there is` provided a ypair of metallic membersy I3 which serve as supports for the mandrel, as rigid mechanical connections between straps 1 and the supporting walls I, and as electrical conducting elements, as will be more clearly apparent hereinafter. Members I3 are preferably formed as bars which are rectangular in cross-section, each having a circular threadedshank or extension Il. These bars are disposed between the depending ends of straps 1 and are rigidly secured thereto by means of bolts 8 above mentioned. The reduced extending shanks of the bars extend through insulating washers I5, insulating bushings (not visible), and supporting walls I. 'Ihe shoulder I l formed on each of the bars abuts against the innermost insulating washer and a nut Il threaded upon each shank Il securesthe bar rmly to the supporting wall. A pair of thumb nuts I8 render the extending ends of the bars useful as binding post terminals for the de.- vice.

It will be noted that the members or bars I3 are diametrically opposite the attachment extensions 9 and serve. in conjunction with the extensions to rigidly secure the mandrel 2 and its supported winding to the end walls. By virtue of Al U their being positioned beneath the supporting mandrel, bars I3 support the weight of the mandrel and the Winding. The bars being rigid, and being so rigidly secured toend walls, a very strong device results. In the event that more than one attachment extension 9 is provided on each strap, they may be arranged so as to be substantially evenly spaced with the members I3, so as to give substantially uniform peripheral connection of the mandrel to the end walls.

In addition to the above-mentioned function, bars i3 serve the purpose of extending the terminals of the resistance winding to points exterior of the device and serve as binding post terminals. rihis construction is a very important feature of the invention, since it results in a mechanically strong and durable device of simple construction.

The slide bar 4 is preferably rectangular in cross section and has diminished circular threaded ends i9 which extend through insulating washers 2li, insulating bushings (not visible) and the end walls l. The shoulders 2l of this bar abut against the innermost washers, and nuts '22, which are threaded upon the threaded ends I9, serve to securely assemble the elements together. Bar d is thus rigidly secured between the upper portions of the end walls. One end of bar 4 serves as a terminal binding post for the device and to that end suitable thumb nuts 23 are provided.

Coming now to the specific construction of the slidable contact member 5, which is an important feature of the invention, and referring more particularly to Figs. 2 to 4, this member comprises a molded insulating body 24 having a central portion 25 and opposed downwardly extending wing portions 26. Portion 24 is formed to provide a deep groove or recess 27, which is of such size and shape as to snugly receive the slide bar 4. Wing portions 26 are formed to provide co-axial grooves 28 which extend in crossed perpendicular relation to groove 21. The co-axial grooves 28 are of such size and shape as to snugly receive a substantially U-shaped contact blade assembly 29. Preferably, this assembly comprises a plurality of bent spring fingers or blades disposed in superposed relation, as illustrated clearly in Fig. 2. A cross-shaped contact element 3|) is provided, the free opposed spring fingers of which are adapted to slidably and resiliently engage the under surface of slide bar 4 so as to make good electrical contact therewith. Element 30 is superposed upon the contact blade assembly and is rigidly secured therewith to the insulating body 24 by suitable screws 3i or the like. The depending ends of blades 29 resiliently engage the resistance winding 3, as indicated clearly at 32. While the contact blades preferably have a substantially inverted U-shaped form, it will be apparent that they may take any other suitable form.

Heretofore, a common objectionable characteristic of rheostats of this class has been that the Contact fingers or blades which engage the resistance winding are not so rigidly held as to prevent backlash or lost motion. In other words, when the slider is moved, there is oft-times considerable lost-motion before the contact fingers start to move, especially when the direction of motion of the slider isy reversed. This objection is eliminated by the present invention due to the fact that the contact fingers are snugly seated in a recess or groove and rigidly secured therein. This is shown perhaps more clearly in Fig. 4.

The side walls which define the grooves of wing portions 2i snugly embrace the contact blades or fingers so as to prevent any backlash. It will also be apparent that the slider assembly is very compact and neat appearing. Moreover, its simple construction renders it susceptible to sconomic manufacture. The opposite sides of the central portion 2l of the slider body are on a line with the slide bar and are shaped so that the body may be readily grasped by an operator to move the slider along the slide bar 4. This ccnstruction facilitates operation of the device. It is also important to note that wing portions I8 substantially cover the blade assembly Il and protect the operator from contact therewith.

Figs. 5 to 7 illustrate a modined form of device in which sliding movement of the slider is had by rotation of a screw shaft. In this instance,

the supporting mandrel 2a and its supported winding 3a are secured between the end walls la in the same manner as has been described above. Only the upper portion of the device is modified to accommodate the screw shaft. The slide bar 4a in this case takes the form of a hollow member, within which the screw shaft Il is rotatably disposed. Although, the slide bar may take any suitable hollow form, it is preferably formed as an inverted channel, as illustrated more clearly in Fig. 6. A pair of metallic inserts 84 and are inserted within the ends of the channelshaped slide bar and serve to support the same. The inserts may be retained by force fitting them in the slide bar or they may be attached to the bar in any desired manner. Insert 34 has an extending threaded shank 38 which passes through the insulating washers 20a, an insulating bushing (not visible), and the associated end wall la. A nut 22a secures the elements together. The thumb nuts 28a, which are threadedly mounted on shank 36, render the extending shank usable as a terminal bindingpost. One end of the screw shaft 33 is reduced in diameter and journaled in insert 34, as illustrated clearly as 31.

The insert 35 has a central longitudinal opening therethrough through which the reduced end 38 of the screw shaft extends. The insert also has a reduced threaded portion 39 which extends through insulating washers 48 and an insulating bushing 4I. A nut 42, which is threaded upon portion 39, serves to secure the parts together. A hand wheel 43 is xedly carried upon the end of shank 38. It will be apparent that by means of the above-described structure, the channelshaped slide bar is securely mounted between the end walls and the screw shaft 33 is rotatably mounted within the slide bar. By having the screw shaft thus mounted, it is inconsplcuous and is, in fact, invisible during -normal casual observance. Prior art devices of this type have commonly employed separated slide bar and screw shaft elements, which not only render the device bulky but detract from its appearance.

The slidable contact assembly 5a is generally similar to that above described. This assembly The extending resilient fingers M are adapted to engage the lower depending edges of the channelshapedslide bar,asillustratedclearlyin!igs.6 and 7. In order to accommodate fingers Il, the molded body is recessed at Il. A centrally-disposed threaded pin 4l passes through the constituent elements of the contact blade assembly and is secured thereto by means of suitable lock nuts 41. The upper end of this pin engageathe spiral groove of the screw shaft, as shown clearly in Fig. 6.

We have discovered that by making the pitch of the spiral groove of the screw shaft relatively large, we are able to provide a device which may be used without modification or adjustment either as a screw type device or as a plain "slider type device. Pin engages the screw shaft at all times and the slider is, therefore, operatively connected with the screw shaft continuously. By using a relatively large screw pitch. we are able to obtain proper adjustment of the slider by rotation of the screw through the medium of hand wheel 43 or by direct manipulation of the slider by grasping the molded body and moving it along the slide bar. If the screw shaft has a diameter of inch, the pitch should be approximately one turn per inch to give anvangle of approximately 45 degrees to the spiral groove. With diil'erent sized shafts, the pitch may be varied accordingly. Heretofore, in devices of this nature, which may be operated either as screw" type devices or as plain slider type devices, it has been the practice to utilize constructions wherein the slider must be freed from operative connection to the screw shaft in order to slide it manually along the slide bar. This, of course, involves a more or less complicated structure and necessitates additional manual operation to release the slider from the screw shaft. The present structure is simple and requires no releasing of the slider, but at the same time enables the desired selective operation as above stated'.

Although the essential features of the invention have been illustrated in their preferred forms herein, as applied to the two general types of slide rheostats, it will be understood that changes and modifications in the details of these features may be resorted to without departing from the spirit and scope of the invention.

We claim:-`

l. In a rheostat, a resistance winding, a slide bar spaced from said winding and extending longitudinally thereof, means for supporting said winding and said slide bar, and a slidable contact member carried by said bar, said member comprising a solid insulating body having a central vportion and opposed wing portions extending downward, said central portion having a groove for receiving said bar so that said body saddles said bar, saidi wing portions having coaxial grooves in crossed perpendicular relation with said first groove and immediately adjacent thereto, a substantially inverted U-shaped contact blade seated in said coaxial grooves and underlying said bar, and a contact finger carried by said blade and slidably engaging said bar, the depending ends of said blade slidably engaging said winding, said contact blade being snugly embraced by the walls of said coaxial grooves, whereby backlash or lost motion of the contact blade is substantially prevented.

2. In a rheostat, a resistance winding, a hollow slide bar spaced from said winding and extending longitudinally thereof, a rotatable screw shaft within said hollow slide bar, means for supporting said winding, said slide bar, and said screw shaft, anda slidable contact member carried by said slide bar, said member comprising a screwengaging member and contact blades slidably engaging said resistance winding and sad slide bar.

3. In a rheostat, apresistance winding, an inverted channel-shaped slide bar spaced from said winding and extending longitudinally thereof, a rotatable screw shaft within said channel-shaped sl'de bar. means for supporting said winding, said slide bar, and said screw shaft, and a slidable contact member carried by said slide bar, said member comprising a screw-engaging member and contact blades slidably engaging said resistance winding and the depending edges of said -slide bar.

4.'In a rheostat, a resistance winding, a hollow slide bar spaced from said winding and extending longitudinally thereof, a rotatable screw shaft of predetermined large pitch within said hollow slide bar, means for supporting said winding, said slide bar, and said screw shaft, and a sldable contact member carried by said slide bar, said member comprising a screw-engaging member and contact blades slidably engaging said resistance winding and said slide bar, whereby said contact member may be slidably moved by manually sliding the same or by rotating said screw shaft.

5. In a rheostat, a resistance winding, a hollow slide bar spaced from said winding and extending longitudinally thereof, a rotatable screw shaft within said hollow slide bar, means for supporting said winding, said slide bar, and said screw shaft, and a slidable contact member carried by said slide bar, said member comprising an insulating body having crossed grooves, one of which receives said bar with the screw shaft therein, a screw-engaging member, and a contact blade Jseated in another of said grooves and electrically associated with said resstance'winding and said slide bar.

6. In a rheostat, a resistance winding, an inverted channel-shaped slide bar spaced from said winding and extending longitudinally thereof, a rotatable screw shaft within said channel-shaped slide bar, means for supporting said winding, said slide bar, and said screw shaft, and a slidable contact member carried by said slide bar, said member comprising an insulating body having a deep groove and a shallow groove in crossed perpendicular relation to each other, said deep groove receiving sa'd bar with the screw shaft therein,

inverted-U-shaped Contact blade seated in said shallow groove and electrically associated with said resistance winding and the depending edges of said slide bar.

7. In a rheostat, a pair of end brackets connected together at their top portions by a slide bar, an insulating mandrel disposed between said brackets but having its ends free of mechanical attachment to said brackets, a resistance winding wound on said mandrel and terminating short of the ends thereof, a slider contact member mounted on said slide bar and slidably engaging said winding, a flat metallic strap wrapped tightly about said mandrel at each end of said winding and serving to secure the winding on the mandrel, and a rigid metallir` bar extending longitudinally beneath each end portion of said mandrel through the corresponding end bracket and rigidly attached to the lower portions of -the whereby said rigid bars secure the lower portions of said brackets to said straps, cooperate with said straps to support said mandrel and its `winding firmly between the brackets, and electrically connect the ends of said winding to th outer terminal ends of the bars.

8. In a rheostat, a pair of fiat plate-like end brackets connected together at their top `portions by a slide bar, an insulating mandrel disposed between said brackets but having its ends free of mechanical attachment to said brackets, a resistance winding wound on said mandrel and terminating short of the ends thereof, a slider contact member mounted on said slide bar and slidably engaging said winding, a nat metallic strap wrapped tightly about said mandrel at each end of said winding and serving to secure the winding on the mandrel, each said strap having an attachment extension secured to and insulated from the corresponding end bracket, and a rigid metallic bar extending longitudinally beneath each end portion of said mandrel through the corresponding end bracket and rigidly attached to the lower portions of the corresponding strap and the said bracket but insulated from the latter, each said rigid bar being spaced from the corresponding attachment extenson and formed at its outer end to serve as a terminal. whereby said extensions and said rigid bars secure said brackets to said straps at spaced points and cooperate with the straps to support said mandrel and its winding rmly between the brackets, and said bars electrically connect the ends of said winding to their outer terminal ends.

9. In a rheostatga resistance winding, a slide bar spaced from said winding and extending longitudinally thereof, means for supporting said winding and said bar, a slidable contact member carried by said bar, said member comprising a solid insulating body having a 'deep longitudinal groove and a shallow transverse groove immedi ately adJacent each other, said body saddling said bar with the bar seated in said longitudinal groove, and an inverted U-shaped contact'blade seated in said transverse groove and electrically associated with said bar and having-its depending ends in sliding engagement with said winding, said contact blade being snugly embraced by the side walls oi' said transverse groove. whereby backlash or lost motion of the contact blade is substantially prevented.

EDWIN W. KIEFABER.

JOSEF DOElEtl't` THOMAS BARCLAY WHITSON. WILLIAM B. CREAGMILE. 

